Artificial vascular graft

ABSTRACT

The invention relates to an artificial vascular graft comprising a primary scaffold structure encompassing an inner space of the artificial vascular graft, said primary scaffold structure having an inner surface facing towards said inner space and an outer surface facing away from said inner space, a coating on said inner surface, wherein a plurality of grooves is comprised in said coating of said inner surface. The primary scaffold structure comprises further a coating on said outer surface. The primary scaffold structure and the coating on said inner surface and on said outer surface are d designed in such a way that cells, in particular progenitor cells, can migrate from the periphery of said artificial vascular graft through said outer surface of said coating, said primary scaffold structure and said inner surface to said inner space, if the artificial vascular graft is used as intended. The invention relates further to a method for providing said graft.

FIELD OF THE INVENTION

The present invention relates to an artificial vascular graft having astructured surface. The invention further relates to a method forproviding such a graft.

BACKGROUND OF THE INVENTION

The prevalence of arterial disease is increasing in many countries dueto the ageing of society. This trend is of particular importance foratherosclerotic vascular diseases such as coronary and peripheralvascular diseases, which are leading causes of death in the westernworld. In general, their treatment and therapy involves a bypass byusing the autologous saphenous vein for treatment of the lower limpartery (Tyler et al.; J. Vasc. Burg.; 11:193-205; 1990) or the internalmammary artery for a coronary artery bypass (Cameron et al.; N. Eng. J.Med.; 334:216-219; 1996). One major drawback of venous grafts, however,is occlusion (stenosis), which is a consequence of systemicpressure-induced tissue degeneration, whereby one-third of vein graftsare occluded within 10 years. Furthermore, half of those show markedatherosclerotic changes (Raja et al.; Heart Lung Circ.; 13:403-409;2004).

An increasing amount of people (up to 30% according to WHO report oncardiovascular diseases 2010) who require cardiac surgery, a vascularsurgical bypass or even a dialysis shunt, cannot be provided withsuitable autologous bypass material, due to pre-existing diseases orbecause the bypass material has already been used in previous surgery.Thus, the demand on an artificial vascular replacement material, whichcomprises analogous characteristics as the native counterpart, isincreasing.

Beside the urgent need for small diameter grafts (as for the coronaryarteries or peripheral blood vessels), there is also a considerable lackof replacement materials concerning large diameter vessels (as for adiseased aorta or for the repair of congenital cardiovascularmalformations).

Existing artificial vascular prostheses have serious limitations. Onemajor problem concerning synthetic materials used as vascularsubstitutes is the patency rate of the grafts due to thrombogenicity andgraft occlusion.

Particularly, the tissue engineered small-diameter vascular graftscomprise several severe shortcomings (Teebken and Haverich; Graft; 5;14; 2002), despite the development of many strategies to fabricatevascular substitutes with anti-thrombogenic properties.

Early approaches focused on surface coating of synthetic grafts byseeding endothelial cells directly onto the vascular prosthesis prior toimplantation. However, these synthetic grafts still induce low-levelforeign body reaction and chronic inflammation and are associated withan increased risk of microbial infections (Mertens et al.; J. Vasc.Surg.; 21:782-791; 1995).

More recent strategies focused on the creation of complete autologous,living vascular substitutes using a three-dimensional temporary vehicleseeded with autologous cells (smooth muscle cells and endothelial cellsin order to line the inner lumen), which are harvested and cultivated.After proliferation in sufficient numbers, the cells are seeded onto thethree-dimensional scaffolds (based on synthetic or natural material) andexposed to a physiological in vitro environment in a bioreactor system.After several weeks the tissue formation and maturation is completed andthe vascular substitutes are ready for implantation. Optionally anon-scaffold based vascular tissue engineering concept via cell sheetsis used. One of the main disadvantages is the time consumingpreparation, which renders these artificial grafts useless for patientsin need of such an artificial graft on short notice, and restricts theapplication to non-urgent patients.

An overview of scaffold materials used in crating grafts has beenpublished by Schmidt and Hoerstrup. (M. Santin (ed.); Strategies inRegenerative Medicine; Chapter 7; DOI 10.1007/978-0-387-74660-9_7).

Natural scaffolds employed include, inter alia, tanned bovine carotidarteries, polyethylene terephthalat (Dacron® DuPont) meshes embeddedinto the collagen or a collagen biomaterial derived from the submucosaof the small intestine and type 1 bovine collagen.

Furthermore, decelluarized tissues fabricated from either vascular ornon-vascular sources were applied and implanted without any in vitrocell seeding, with the assumption that they will be recelluarized byhost cells in vivo. However, significant shrinkage was observed indecelluarized vessels as a result of proteoglycans being removed fromthe tissues during the decelluarization process. Additionally, anadverse host response, aneurysm formation, infection and thrombosisafter implanting decelluarized xenografts were observed.

As permanent synthetic scaffolds, polyurethane (PU) and loosely woven,relatively elastic, polyethylene terephthalat (Dacron® DuPont) basedscaffolds were applied. However, the major limitation of these materialsis lack of compliance. When used for repairing or replacing smallerdiameter arteries, these grafts may fail due to occlusion by thrombosisor kinking, or due to an anastomotic or neointimal hyperplasia.Furthermore, expansion and contraction mismatches can occur between thehost artery and the synthetic vascular prosthesis, which may result inanastomotic rupture, stimulated exuberant cell responses as well asgraft failure due to disturbed flow patterns and increased stresses.

Concerning biodegradable synthetic scaffolds, several attempts were madeto apply biodegradable polymers as temporary mechanical support for invitro generated tissues.

Particularly polyglycolic acid (PGA) or copolymers thereof, polylactidacid (PLA) and Poly-ε-caprolactone (PCL) were used as biodegradablepolymers. The biodegradable synthetic material serves as a temporaryscaffold and guides tissue growth and formation until the neo-tissuedemonstrates sufficient mechanical properties, whereby—in theory—thescaffold will degrade completely after a certain time, providing a totalautologous vascular graft. However, the difficult control of the ratioof degeneration, which has to be proportional to the tissue development,is one of the main drawbacks of these grafts. As a consequence, if thespeed of material degradation is faster than regeneration of the tissuein the vascular graft, the graft may rupture.

There are many drawbacks considering the provision of artificial grafts.For example, matching the mechanical properties of large-diametervessels for the replacement of the aorta—due to high pressure changes—isdifficult. Such mechanical properties could only be obtained in long invitro culture times, which render clinical application almostimpossible. Furthermore, a long in-vitro culture time increases therisks of infection and cell dedifferentiation.

The demand for small diameter artificial grafts is very high. Especiallywith respect to the tissue engineering of small-diameter blood vessels,however, the mentioned problems could not be solved satisfactorily.These artificial grafts remain a particular challenge due to the lowerflow velocity compared to large-diameter vessels. Bearing in mind thelaw of Hagen-Poiseuille, the volume of the flow is highly dependent onthe radius of the tube, considering the flow characteristics ofvoluminal laminar stationary flows of incompressible uniform viscousliquids through cylindrical tubes with constant circular cross-sections.

The special problem associated with small-diameter grafts appears to berelated primarily to the development of a fibrinous pseudointima, withgradual thickening that leads to thrombotic occlusion of the graft.However, patency rates of artificial small-diameter grafts areunacceptable in comparison to autologous vein and arterial grafts(Teebken and Haverich; Graft; 5: 14; 2002).

Thrombosis due to the reaction with foreign bodies or lack ofendothelial cells, intimal hyperplasia caused by inflammatory reactionand compliance mismatch of the native vessel and the prosthetic graft atthe anastomosis site are unsolved problems of particular importance.

In summary, existing grafts—especially small diameter grafts—have severedrawbacks such as the amount of time to produce in vitro grafts (e.g.via seeding of endothelial cells), thrombosis or the lack of thenecessary stability.

Therefore, the provision of artificial grafts, in particularsmall-diameter artificial grafts, is highly desirable, in order toprovide means of an optimal therapeutic artificial vascular graft, whichcan be used for a cardiovascular bypass operation for patients lackingsuitable autologous bypass material.

It is an object of the present invention to improve on the abovementioned state of the art, in particular to provide safe andefficacious artificial grafts, which could be used instantly afterunpacking, without the limitations of the existing artificial grafts, aswell as a method to produce said grafts. This objective is attained bythe subject matter of the independent claims.

BRIEF SUMMARY OF THE INVENTION

The invention provides an artificial vascular graft featuring a primaryscaffold structure encompassing an inner space of the artificialvascular graft. The primary scaffold structure has an inner surfacefacing towards the inner space and an outer surface facing away from theinner space. The artificial vascular graft further comprises a coatingon the inner surface of the primary scaffold structure. The coating,situated on the inner surface of the primary scaffold structure, has aninner coating surface facing towards the inner space of the artificialvascular graft. Additionally, the artificial vascular graft comprises aplurality of grooves in the coating of the inner surface of the primaryscaffold structure. These grooves are situated on the inner coatingsurface of said coating, whereby the inner coating surface of thecoating faces towards the inner space of the artificial vascular graft.

The primary scaffold structure comprises further a coating on said outersurface. The primary scaffold structure and the coating on said innersurface and on said outer surface are designed in such a way that cells,in particular progenitor cells, can migrate from the periphery of saidartificial vascular graft through said outer surface of said coating,said primary scaffold structure and said inner surface to said innerspace, if the artificial vascular graft is used as intended.

The artificial vascular graft comprises at least two openings.

The artificial vascular graft of the invention is intended to replacediseased or dysfunctional vascular tissue in a patient. Thereby, theopenings of the graft are connected with one or more blood vessels.Particularly, the artificial vascular graft is used as a substitution ofa part of a natural blood vessel, therefore, after removal of a part ofthe natural blood vessel, the ending of a blood vessel remaining in thepatient is connected with one opening of the artificial vascular graft,whereby an other ending of a blood vessel is connected with anotheropening of the artificial vascular graft. This allows a flow of bloodfrom one opening of the artificial vascular graft through to the otheropening.

In some embodiments, the artificial vascular graft comprises more thantwo openings. By way of non-limiting example, the artificial graft cantake the form of a Y-shaped vessel (a junction or furcation). ThisY-shaped graft is similarly intended to be connected to blood vesselsfor blood flow.

The inner surface of the coating, which comprises the plurality ofgrooves, will be in contact with blood flowing through the artificialvascular graft, when the artificial vascular graft is used as intended.

Generally, the primary scaffold structure offers the necessary stabilityand structural integrity and supports the coating. In one embodiment,the primary scaffold structure comprises a coating on the inner and theouter surface of the primary scaffold structure. Thus, the coatingencompasses the primary scaffold structure.

The artificial vascular graft with the features according to theinvention may be used, inter alia, as an implant, in particular forblood vessels or cardiac valves. It may be further used as a dialysisshunt or as a tube for blood in and out flow in a life support machine.

In some embodiments, the primary scaffold structure and/or the coatingis characterized by a generally tubular shape. The tubular shape may bebranched, comprising one additional tubular branch (yielding a formcomparable to the letter “Y”) or more tubular branches.

In some embodiments, the primary scaffold structure comprises agenerally tubular shape having an outer diameter in the range of about1.5 mm to 40 mm, in particular of about 1 mm. 1.5 mm, 2 mm, 3 mm, 4 mm,5 mm, 7.5 mm, 10 mm, 12.5 mm to 15 mm.

In some embodiments, the primary scaffold structure comprises agenerally tubular shape having an outer diameter in the range of about3.5 mm to 40 mm. In some embodiments, the primary scaffold structurecomprises a generally tubular shape having an outer diameter in therange of about 3.5 mm to 15 mm.

The outer diameter of the primary scaffold structure is the maximaldistance of two points situated on the outer surface of the primaryscaffold structure, measured through the center of the tubular primaryscaffold structure and in the plane, which extends vertical to thelongitudinal extension direction of the primary scaffold structure.

In some embodiments, the primary scaffold structure comprises agenerally tubular shape with an outer diameter in the range of about 6mm to 40 mm, in particular of about 6 mm, 7 mm, 8 mm, 9 mm, 10 mm, 11mm, 12 mm, 13 mm, 14 mm to 15 mm for use as a large-size diameterartificial vascular graft. In a further embodiment, the primary scaffoldstructure comprises a generally tubular shape with an outer diameter inthe range of about 1.5 mm, 2 mm, 3 mm, 4 mm, 5 mm or 6 mm for use as asmall-size diameter vascular artificial graft.

In one embodiment, the primary scaffold structure comprises a generallytubular s ape with an outer diameter in the range of about 1.5 mm and 4mm for use as a small-size diameter artificial vascular graft. In oneembodiment, the primary scaffold structure comprises a generally tubularshape with an outer diameter in the range of about 4 mm and 6 mm for useas a small-size diameter artificial vascular graft.

In one embodiment, the primary scaffold structure comprises a generallytubular shape with an outer diameter in the range of about 3.5 mm and 5mm, in particular of about 4.5 mm for use as a small-size diameterartificial vascular graft.

In some embodiments, the thickness of the primary scaffold structure(i.e. the distance between the inner and outer surface of the primaryscaffold structure) is between 0.05 mm and 1 mm, in particular between0.1 mm and 0.3 mm. In another embodiment, the thickness is about 0.2 mm.In other words, the term “thickness” in this context refers to thedifference between the outer diameter and the inner diameter of theprimary scaffold structure, whereby the inner diameter of the primaryscaffold structure is the maximal distance of two points situated on theinner surface of the primary scaffold structure, measured through thecenter of the tubular primary scaffold structure and in the plane, whichextends vertical to the longitudinal extension direction of the primaryscaffold structure.

In some embodiments, the primary scaffold structure has a length,measured in the longitudinal extension direction of the primary scaffoldstructure, of at least 1 cm. In another embodiment, the primary scaffoldstructure has a length, measured in the longitudinal extension directionof the primary scaffold structure, between 8 cm to 40 cm, in particularbetween 15 cm to 20 cm.

In some embodiments, the primary scaffold structure exhibits aphysiological compliance comparable to a native vessel in order towithstand hemodynamic pressure changes without failure. Thus, theprimary scaffold structure comprises a material that is characterized bya compliance in the range of 400 to 1000%/2.93 kPa (22 mm Hg), inparticular in the range of 600 to 800%/2.93 kPa (22 mm Hg).

Unless otherwise indicated, the term “compliance” refers to the abilityof the primary scaffold structure and/or the coating to distend andincrease its volume with increasing inner pressure, when the artificialvascular graft is used as intended. Furthermore, the term “compliancerefers” to the ratio of the diameter change of the primary scaffoldand/or the coating as the artificial vascular graft expands in theradial direction in response to a given change in the inner pressure,and the values for compliance referred to below result from dynamic, invitro testing.

In one embodiment, the burst pressure of the primary scaffold structureand the coating is higher than 133.32 kPa (1000 mm Hg).

In some embodiments, the primary scaffold structure comprises a materialwith a high tensile strength, in order to provide mechanical support tothe artificial vascular graft, whereby the material of the primaryscaffold structure is able to recoil to an original state after asymmetrical, radial expansion perpendicular to the longitudinal axis ofthe artificial vascular graft, wherein said radial expansion is in therange of 5% to 40%, in particular of 15% to 20%, with respect to theoriginal outer diameter of the primary scaffold structure or theoriginal inner diameter (see definition below) of the coating. In thefollowing, it will be referred to as a flexibility of 5% to 40%, inparticular of 15% to 20%. The term “original state” refers to thediameter size of the outer diameter of the primary scaffold structure orthe inner diameter of the coating before use, particularly beforeexposing the graft to pressure. Thus, the primary scaffold structurecomprises a flexible, resilient material, which enables recoil in orderto prevent aneurysm formation.

In summary, the primary scaffold structure comprises mechanicalproperties similar to those of its natural counterpart, and provides aresponse to physiological changes by means of adequate vasoconstrictionand relaxation when used as intended. That is, it functions withoutundue bulging or aggravated mismatching phenomena leading to graftfailure.

In some embodiments, the primary scaffold structure comprises aplurality of holes, which are suited for a migration of cells, compoundsand gases. In particular O₂ and CO₂, vascular growth factors, allhumoral agents, progenitor cells capable of differentiating towardsendothelial lineages and macrophages are allowed to migrate through theprimary scaffold structure. In other words, the primary scaffoldstructure comprises a “perforated” structure, whereby the holes providean opening, which reaches from the outer surface to the inner surface,thus, through the primary scaffold structure. Any kind of symmetricforms (for example round, oval, rectangular, etc.) or asymmetric formsare possible, as long as they allow said migration through the holes,while maintaining the necessary stability and structural integrity ofthe scaffold structure. Furthermore, a wire structure—comparable tocellulose—may be applied providing an interconnected hollow space in theprimary scaffold structure. Thus allowing said migration. In otherwords, said “perforated” structure may comprise holes in form of astraight or branched tunnel or in form of an interconnected hollow spaceallowing said migration. In some embodiments, the diameter of the holesranges from about 20 μm to 500 μm, in particular from about 20 μm to 300μm. In some embodiments, the diameter of the holes ranges from about 35μm to 50 μm. Also larger and smaller diameters may be employed.

In some embodiments, the diameter of the holes ranges from about 10 μmto 500 μm, in particular from about 10 μm to 200 μm. In someembodiments, the diameter of the holes ranges from about 10 μm to 100μm. Also larger and smaller diameters may be employed.

In some embodiments, the primary scaffold structure comprises a meshstructure, in order to support the coating material and to allow theabove discussed migration of cells, compounds and gases. In oneembodiment, the primary scaffold structure may take the form of aknitted, braided or woven mesh structure. The primary scaffold structuremay be appropriately crimped to provide the required resiliency andcompliance, so that the primary scaffold structure is capable of aresilient radial expansion in a manner mimicking the complianceproperties of a blood vessel, as discussed above.

In some embodiments, the primary scaffold structure may take the form ofa wire mesh. In one embodiment, the wire thickness can be between 20 μmto 500 μm, in particular between 50 μm to 300 μm. In another embodiment,the wire thickness can be between 100 μm to 200 μm. In a furtherembodiment, the wire thickness can be between 50 μm to 150 μm.

In some embodiments, the maximal distance between neighboring wires canrange from about 20 μm to 500 μm, in particular from about 100 μm to 300μm. In one embodiment, the maximal distance between neighboring wirescan range from about 20 μm to 100 μm. In one embodiment, the maximaldistance between neighboring wires can range from about 35 μm to 50 μm.Thus, the wire mesh structure provides “holes” in the surface with anarea of about 400 μm²-250 000 μm², depending on the selected maximaldistances. The wire mesh may have the form of a criss-crossed pattern ormay comprise interconnected loops. In some embodiments, the maximaldistance between neighboring wires is identical.

In some embodiments, the maximal distance between neighboring wires canrange from about 10 μm to 500 μm, in particular from about 10 μm to 200μm. In one embodiment, the maximal distance between neighboring wirescan range from about 10 μm to 100 μm. Thus, the wire mesh structureprovides “holes” in the surface with an area of about 100 μm²-250 000μm², depending on the selected maximal distances. The wire mesh may havethe form of a criss-crossed pattern or may comprise interconnectedloops. In some embodiments, the maximal distance between neighboringwires is identical.

In some embodiments, the primary scaffold structure and/or the coatingcomprise or consist of a biostable material. The term “biostable”material, used in context of this invention, is to be understood as amaterial with the ability to essentially maintain its physical andchemical integrity after implantation in living tissue. It has to beunderstood that a slight degradation (respectively a slow decomposition)of the applied material over a long period of time is considered as“biostable” in the context of the present specification.

In some embodiments, the primary scaffold structure and/or the coatingcomprise or consist of a degradable material. The term “degradable”material, used in context of the present specification, is to beunderstood as a material that will be broken down (degraded)—afterimplantation in living tissue during the course of time, in particular50% of the original material will be degraded within between 3 to 24months after implantation.

Thus, “biostable” material is to be considered as physically andchemically inert over a long period of time, whereby “degradable”materials will degrade over time.

In one embodiment, the primary scaffold structure comprises or consistsof a corrosion resistant, biostable metal, in particular unalloyedcommercial pure titanium (cp-Ti). The cp-Ti may be employed in differentcommercial available grades, in particular grades 1 to 4 (according toASTM (American Society for Testing and Materials) F67-06: Grade 1-UNS(Unified Numbering System) R50250; Grade 2-UNS R50400; Grade 3-UNSR50550; and Grade 4-UNS R50700).

In another embodiment, the primary scaffold structure comprises orconsists of a corrosion resistant, biostable metal alloy, in particulara high grade steel, a Cobalt based alloy, a Nickel based alloy or aTitanium based alloy. In some embodiments, the primary scaffoldstructure comprises a CoCrMo- or CrNiMo-alloy.

In some embodiments, the primary scaffold structure comprises orconsists of a biostable, corrosion resistant shape memory alloy. Theshape memory alloy comprises so-called “superelastic” properties. Thus,the shape memory alloy can undergo large deformations under stress andthen instantly revert back to the original shape when the stress isremoved. The shape memory alloy comprises a flexibility of 5% to 40%, inparticular of 15% to 20%. Furthermore, the shape memory alloy comprisesa high durability, namely a very good strain-controlled fatigueperformance. Thus, fatigue failures due to expansion and recoil of theshape memory alloy on basis of changing pressure inside the artificialgraft, if it is used as intended, could not be observed over a prolongedperiod of time.

In some embodiments, the shape memory alloy comprises or consists of atitanium-palladium-nickel, nickel-zirconium-titanium,nickel-iron-zinc-aluminum and iron-manganese-silicon alloy.

In another embodiment, the primary scaffold structure comprises orconsists of a shape memory alloy with 50 to 60% nickel (Reference) and40 to 50% titanium (Balance), in particular 54.5% to 57.0% nickel(Reference) and 43.0 to 45.5% titanium (Balance) according to theStandard Specification for Wrought Nickel-Titanium Shape Memory Alloysfor Medical Devices and Surgical Implants (ASTM F2063-05; Nitinol).

In a further embodiment, the nickel-titanium alloy (Nitinol) comprises aflexibility of 5% to 40%, in particular of 15% to 20%. Thus, the primaryscaffold structure is able to recoil after a symmetrical radialexpansion of 5% to 40%, in particular of 15% to 20%, with respect to theoriginal diameter of the primary scaffold structure. Furthermore, theprimary scaffold structure material comprises compliance in the range of600 to 800%/2.93 kPa (22 mm Hg).

In some embodiments, the primary scaffold structure and/or the coatingcomprise or consist of a polymer material.

In some embodiments, the polymer material comprises or consists of asynthetic, biostable polymer like polyethylene terephthalate (PET),polypropylene (PP), polytetra-fluoroethylene (PTFE)), expandedpolytetra-fluoroethylene (ePTFE), polyacrylnitril (PAN) and polyurethane(PU).

In some embodiments, the polymer material comprises or consists of abiopolymer like a polypeptide or a polysaccharide, whereby the term“biopolymer” has to be understood as a polymeric material formed byliving organisms. In some embodiments, the biopolymer comprises orconsists of a biostable material like biostable collagen, in particularCollagen IV, or biostable cellulose.

In some embodiments, the polymer material comprises or consists of ashape memory polymer material, in particular polyurethane (PU),polyethylene terephthalate (PET), polyethyleneoxides (PEO), polystyrene,polytetrahydrofurane or polynorborene, whereby the shape memory polymermaterial comprises comparable characteristics as already discussed withrespect to the shape memory alloys.

In some embodiments, the primary scaffold structure comprises a shapememory polymer material, which is reinforced by a shape memory metalalloy, in particular Nitinol.

In one embodiment, the primary scaffold structure comprises or consistsof an elastomeric synthetic polymer or biopolymer material, e.g. apolyurethane elastomer or composite fibers that act in an elasticfashion. Further—not limiting—examples are fluoroelastomers (FKM),perfluoroelastomers (FFKM) or tetrafluoro ethylene/propylene rubbers(FEPM) and elastomeric polypeptides.

In some embodiments, the primary scaffold material and/or the coatingcomprise or consist of a degradable synthetic polymer, or a degradablebiopolymer material, in particular, polyglycolic acid (PGA) orcopolymers thereof, polylactid acid (PLA), Poly-ε-caprolactone (PCL) ordextran.

In some embodiments, the primary scaffold structure and/or coatingcomprise or consist of a degradable biopolymer material, for example acellulose material, such as cellulose ester, cellulose acetate ornitrocellulose and their derivatives (celluoid). In some embodiments,the primary scaffold structure and/or coating comprise or consist of adegradable biopolymer material, for example a degradable collagenmaterial.

The above mentioned materials can be used for a primary scaffoldstructure comprising a knitted, braided or woven mesh structure as wellas a wire mesh structure. In particular, the primary scaffold structuremay take the form of a wire mesh made of metal, metal alloy or shapememory alloy. The same applies for the above discussed structurescomprising holes.

In one embodiment, the eSVS MESH® Nitinol-mesh can be used as a primaryscaffold structure, which could be purchased from Kips Bay Medical, Inc.Minneapolis, Minn., USA.

In some embodiments, the primary scaffold structure and the coatingcomprise or consist of a semipermeable material, in particular asemipermeable polymer material, so that cells and gases, in particularO₂ and CO₂, vascular growth factors, all humoral agents, progenitorcells capable of differentiating towards endothelial lineages andmacrophages, can migrate through the primary scaffold structure and thecoating to the inner coating surface of the coating, whereby the primaryscaffold structure and the coating remains impermeable for the remainingsubstances of blood. The primary scaffold structure and the coating onsaid inner surface and on said outer surface are designed in such a waythat cells, in particular progenitor cells, can migrate from theperiphery of said artificial vascular graft through said outer surfaceof said coating, said primary scaffold structure and said inner surfaceto said inner space, if the artificial vascular graft is used asintended. Reference is made to the detailed explanation above concerningthe semipermeable ability.

The migratory capacity of cells through the primary scaffold structureand the coating on said inner surface and on said outer surface can betested according to the specifics as detailed in the publication of Chenet. al. (see Chen Y, Wong M M, Campagnolo P, Simpson R, Winkler B,Margariti A, Hu Y, Xu Q. “Adventitial stem cells in vein grafts displaymultilineage potential that contributes to neointimal formation.Arterioscler Thromb Vasc Biol. 2013, August; 33(8):1844-51. doi:10.1161/ATVBAHA.113.300902).

The term “semipermeable” according to the invention is to be understoodthat the primary scaffold structure and the coating on the inner andouter surface of the primary scaffold structure are designed in such away that that cells and gases, in particular O₂ and CO₂, vascular growthfactors, all humoral agents, progenitor cells, more particularprogenitor cells capable of differentiating towards endothelial lineagesand macrophages, can migrate through the primary scaffold structure andthe coating to the inner space (lumen) of the artificial vascular graft.If the artificial vascular graft is used as intended, substances ofblood, such as thrombozytes, erythrocytes, leukocytes, cannot migratefrom the inner space of the artificial vascular graft (lumen) throughthe primary scaffold structure and the coating on the inner and outersurface of the primary scaffold structure since platelets, also called“thrombocytes”, will attach themselves on the coating facing the lumenand interconnect with each other providing an “impermeable wall” for theremaining substances of blood. However, cells and gases, in particularprogenitor cells, are still capable to migrate from outside of thevascular graft towards the inner space (lumen)—due to the design of theartificial vascular graft—and through said impermeable wall provided bysaid thrombocytes.

Progenitor cells, such as mesenchymal stem cells, can migrate throughthe layers of other cells especially through thrombocytes or adhaerentcells by deformation and interaction.

The migration of progenitor cells to the lumen is particularly achievedby providing suitable holes, pores or interconnected hollow spaces, asdiscussed above and below of this section, allowing for the migration ofprogenitor cells capable of differentiating towards endothelial lineagesand macrophages, to the inner space of the graft (lumen).

Progenitor cells capable of differentiating towards endothelial lineagesand macrophages, are in particular mesenchymal stem cells, local tissueresidential progenitor cells, especially adventitial residents and fattissue residents such as epicardial progenitors or vein neighboringadventitial progenitors.

Vascular growth factors may migrate into or through the primary scaffoldstructure and the coating on the inner and outer surface from theperiphery of the vascular graft but mainly from the blood inside theartificial vascular graft and enhance the migration of the cells bychemotaxis (the movement of an organism in response to a chemicalstimulus).

In general, the major part of the progenitor cells, which amounts toabout 80%, originate from the periphery of the artificial vascular graftand migrate through the “holes” or hollow spaces in the primary scaffoldstructure material and the coating material and only a small part (20%)stems from the blood inside the artificial vascular graft (see Hu Y, XuQ. Adventitial biology: differentiation and function. ArteriosclerThromb Vasc Biol. 2011 July; 31(7):1523-9. doi:10.1161/ATVBAHA.110.221176). Thus, a larger amount of the necessaryprogenitor cells are provided in the lumen of the graft fordifferentiation processes (as discussed below).

In some embodiments, the primary scaffold structure and/or the coating,in particular the coating, comprise or consist of a material providinghydrogen-bonding facilitating the cell migration (see Xiao Q, Zeng L,Zhang Z, Margariti A, Ali Z A, Channon K M, Xu Q, Hu Y. Sca-1+progenitors derived from embryonic stem cells differentiate intoendothelial cells capable of vascular repair after arterial injury.Arterioscler Thromb Vasc Biol. 2006 October; 26(10):2244-51.

In some embodiments, the primary scaffold structure comprises orconsists of a fibroblast sheet. In some embodiments, the primaryscaffold structure comprises an arterial, respectively venousdecelluarized homograft or xenograft.

In general, the primary scaffold structure and/or the coating may bemanufactured from any biologically acceptable material that possessesthe ability to be shaped into the necessary structure, in particular agenerally tubular structure, which allows for the above mentionedmigration and comprises the required compliance and flexibility, asdescribed above.

The flexibility of the above mentioned materials can be controlled byaltering compositions, by crimping or tempering procedures. Furthermore,in case of wire mesh structures, by variation of the wire diameters orthe distances of neighboring wires etc., so that the primary scaffoldstructure fashioned from this material may mimic the compliance valuesand flexibility of a native blood vessel, in particular in the aspectsof timing, expansion and recoil.

In one embodiment, the coating covers the primary scaffold structurecompletely. In other words, the primary scaffold structure is completelyembedded in the coating material. This prevents, if the artificialvascular graft is used as intended, an attachment of fibroblast andinflammatory cells on the primary scaffold structure. Furthermore, thecoating prohibits an interaction of the material of the primary scaffoldstructure, if the artificial vascular graft is used as intended, withthe surroundings, in particular with blood. In case of a metal or metalalloy material as a primary scaffold structure, the coating prohibitsthe separation of metal ions and the interaction of said ions with thehuman body.

In one embodiment, the coating comprises a generally tubular shape witha length, measured in the longitudinal extension direction of thecoating, which is 2 mm to 20 mm, in particular 4 mm to 10 mm, longerthan the length of the respective primary scaffold structure. Thus, thecoating comprises a projection over the primary scaffolds structure.This projection provides protection, while connecting a blood vesselwith the artificial vascular graft during anastomosis—if the artificialvascular graft is used as intended.

In one embodiment, the material of the coating is able to recoil after asymmetrical, radial expansion of 5% to 40%, in particular of 15% to 20%,with respect to the original diameter of the coating (also referred toas flexibility).

In another embodiment, the coating comprises a material which providessimilar mechanical properties as their native counterpart (e.g. a bloodvessel). Thus, the coating comprises a material characterized by acompliance in the range of 400 to 1000%/2.93 kPa (22 mm Hg), inparticular in the range of 600 to 800%/2.93 kPa (22 mm Hg).

Thus, the coating material comprises an elastic material, which is ableto recoil in order to prevent aneurysm formation, and/or exhibits aphysiological compliance comparable to a native vessel in order towithstand hemodynamic pressure changes without failure, if theartificial vascular graft is used as intended.

In some embodiments, the coating has a generally tubular shape with aninner diameter in the range of about 1 mm to 35 mm, in particular in therange of about 1 mm, 1.5 mm, 2 mm, 3 mm, 4 mm, 5 mm, 7.5 mm, 10 mm, 12.5mm to 15 mm. The inner diameter of the coating is the maximal distanceof two points situated on the inner coating surface of the tubularcoating, measured through the center of the tubular coating and in theplane, which extends vertical to the longitudinal extension direction ofthe tubular coating. In some embodiments, the coating has a generallytubular shape with an inner diameter in the range of about 6 mm to 10 mmfor the use as a large-size diameter artificial vascular graft. In someembodiments, the coating has a generally tubular shape with an innerdiameter in the range of about 1 mm to 6 mm, in particular of about 4 mmto 6 mm for use as a small-size diameter artificial vascular graft. Insome embodiments, the coating has a generally tubular shape with aninner diameter in the range of about 1 mm to 4 mm, in particular in therange of about 1 mm to 3.5 mm for use as a small-size diameterartificial vascular graft. Thus, the diameter of the inner coatingsurface of the coating allows a flow rate of 50 to 200 ml/min, withoutaffecting the pulsation index, which is a factor of lower than fiveafter anastomose.

In some embodiments, the coating has a thickness (whereby thickness isthe difference between the outer and inner diameter of the coating) inthe range of 0.5 mm to 6 mm, in particular in the range of 2 mm to 4 mm.The outer diameter of the coating is the maximal distance of two pointssituated on the outer coating surface of the tubular coating, measuredthrough the center of the tubular coating and in the plane, whichextends vertical to the longitudinal extension direction of the coating.In some embodiments, the coating is symmetrically distributed withrespect to the primary scaffold structure. In other words, the distancefrom the outer surface of the primary scaffold structure to the outercoating surface of the coating is essentially the same as the distancefrom the inner surface of the primary scaffold structure to the innercoating surface of the coating.

In another embodiment, the coating is asymmetrically distributed aroundthe primary scaffold structure. Thus, the coating comprises an innerthickness, which is the difference between the inner diameter of thecoating and the inner diameter of the primary scaffold structure, and anouter thickness, which is the difference between the outer diameter ofthe coating and the outer diameter of the primary scaffold structure,whereby the value of the inner thickness is different to the value ofthe outer thickness. In one embodiment, the outer thickness is largerthan the inner thickness of the coating.

In some embodiments, the primary scaffold structure and/or the coatingcomprise a symmetrical tubular structure. Thus, the primary scaffoldstructure and/or the coating comprise—throughout the tubular artificialvascular graft—a tubular structure with an essentially identical outerdiameter of the primary scaffold structure and/or an essentiallyidentical inner diameter of the coating.

In one embodiment, the coating comprises an inert and sterile material.In another embodiment, the coating comprises an anti-thrombogenicmaterial. In some embodiments, the anti-thrombogenic material can becellulose, Collagen IV, matrigel, heparin coated polymers and IPS(Induced pluripotent stem) cell generated neointima. In someembodiments, the anti-thrombogenic material can comprise ECM components(extracellular matrix), whereby the ECM is composed of three majorclasses, namely structural proteins, like collagen and elastin,specialized proteins, like fibrillin, fibronectin and laminin, andproteoglycans.

In some embodiments, the coating comprises a sterile, anti-thrombogenicand inert material. Thus, the coating is compatible for every patientand there is no need for additional anticoagulation and the artificialvascular graft can be used instantly for an implantation. In someembodiments, the material of the coating is resistant to infection afterimplantation and is designed to avoid inflammation and hyperplasia.

In some embodiments, the coating comprises or consists of a polymer or adegradable polymer, whereby the polymer or degradable polymer issterile, anti-thrombogenic and inert. In some embodiments, the coatingcomprises or consists of a cellulose material, which is biological inertand sterile. In one embodiment, the coating comprises or consists of acellulose material with anti-thrombogenic abilities.

In some embodiments, the coating comprises or consists of a cellulosematerial, which is biologically inert, sterile and anti-thrombogenic.

In some embodiments, the cellulose material of the coating is able torecoil after a symmetrical, radial expansion (also referred to asflexibility) of 5% to 40%, in particular of 15% to 20%, with respect tothe original inner diameter of the coating.

In some embodiments, the cellulose material of the coating exhibits aphysiological compliance comparable to a native vessel in order towithstand hemodynamic pressure changes without failure and, thus,providing compliance in the range of 400 to 1000%/2.93 kPa (22 mm Hg),in particular in the range of 600 to 800%/2.93 kPa (22 mm Hg).

In some embodiments, the cellulose material of the coating comprises asemipermeable ability. Thus, cells and gases, in particular O₂ and CO₂,vascular growth factors, all humoral agents, progenitor cells capable ofdifferentiating towards endothelial lineages and macrophages, canmigrate through the cellulose material towards the inner diameter of thecoating, whereby the coating material remains impermeable for theremaining substances of blood. Thus, the cellulose material—comprising athree-dimensional structure pattern in form of interconnectedfibers—allows for a migration of cells, compounds and gases. Inparticular O₂ and CO₂, vascular growth factors, all humoral agents,progenitor cells, more particularly progenitor cells capable ofdifferentiating towards endothelial lineages and macrophages to migratethrough the cellulose material via the interconnected hollow spacebetween the fibers of the cellulose material.

In other words, the cellulose material comprises “holes” respectively“porous” structure, whereby the interconnected hollow space provide an(indirect) opening, which reaches from the outer surface to the innersurface, thus, allowing said migration. In some embodiments, the meandiameter of the hollow space ranges from about 20 μm to 500 μm, inparticular from about 20 μm to 300 μm. In some embodiments, the diameterof the holes ranges from about 35 μm to 50 μm. Also larger and smallerdiameters may be employed. In some embodiments, the mean diameter of thehollow space ranges from about 10 μm to 500 μm, in particular from about10 μm to 200 μm. In some embodiments, the diameter of the hollow spaceranges from about 10 μm to 100 μm.

Concerning a further discussion of the “semipermeable ability”references is made to the detailed description above.

In some embodiments, the cellulose material of the coating is sterile,inert and comprises semipermeable and anti-thrombogenic abilities, aswell as the above mentioned flexibility and compliance.

In one embodiment, the cellulose is derived from the bacteriaAcetobacter, in particular Acetobacter xylinum strain ATTC 23769 and issterile, inert and comprises semipermeable and anti-thrombogenicabilities, as well as the above discussed flexibility and compliance.

The cellulose fibers derived from said bacteria have a high aspect ratiowith a diameter of 100 nm. As a result, said cellulose has a very highsurface area per unit mass. The fibrous structure consists of athree-dimensional non-woven network of nanofibrils, sharing the samechemical structure as plant cellulose, which is held together by inter-and intra-fibrilar hydrogen bonding resulting in a never-dry hydrogelstate with high strength.

In one embodiment, the primary scaffold structure and the coatingcomprise a flexibility of 5% to 40%, in particular of 15% to 20%, withrespect to the original outer diameter of the primary scaffold structureor the original inner diameter of the coating, and a compliance in therange of 400 to 1000%/2.93 kPa (22 mm Hg), in particular in the range of600 to 800%/2.93 kPa (22 mm Hg). Thus, the coating material iscompatible for every patient and there is no need for additionalanticoagulation and the artificial vascular graft is able to recoil inorder to prevent aneurysm formation and exhibits a physiologicalcompliance comparable to a native vessel in order to withstandhemodynamic pressure changes without failure, if the artificial vasculargraft is used as intended. Particularly preferred is a flexibility of15% to 20%. A too low flexibility will end in stiffness preventing thenecessary arterial like pulsation and a too high flexibility will end ina high material swing ending in turbulent flow leading to restenosis.

In one embodiment, the coating comprises a polymer material, inparticular a cellulose material, comprising the previously describedfeatures and the primary scaffold structure comprises a shape memoryalloy, in particular Nitinol.

In one embodiment, the coating consists of a cellulose materialcomprising the previously described features and the primary scaffoldstructure comprises a shape memory alloy, in particular Nitinol. Theprimary scaffold structure and the coating comprise a flexibility of 5%to 40%, in particular of 15% to 20%, with respect to the original outerdiameter of the primary scaffold structure or the original innerdiameter of the coating, and a compliance in the range of 400 to1000%/2.93 kPa (22 mm Hg), in particular in the range of 600 to800%/2.93 kPa (22 mm Hg).

In some embodiments, the primary scaffold structure comprises holes or amesh structure and is embedded in the coating material, in particular acellulose material, in such a way, that the coating material reachesthrough the “holes” of the primary scaffold structure yielding to astrong connection between the primary scaffold structure and thecoating.

Nevertheless, this has no impact on the semipermeable ability asdiscussed above.

In some embodiments, the coating comprises the same coating material onthe outer surface and the inner surface of the primary scaffoldstructure, which is selected from the above mentioned materials. In someembodiments, the coating comprises different materials on the outercoating surface and on the inner coating surface, whereby each materialis selected from the coating materials discussed above. In oneembodiment, the outer surface comprises a coating of decelluarizedfibroblasts or gelatin, whereby the inner surface comprises a coatingmaterial selected from the above mentioned materials.

In some embodiments, the primary scaffold structure and the coating arecapable of providing a necessary stability after a cutting of theartificial vascular graft (the generally tubular shape will remainintact and particularly no parts of the primary scaffold structure, suchas wire parts of the mesh, will be in contact with living tissue, due tothe coating in which the primary scaffold structure is embedded).

In one embodiment, a plurality of grooves on the inner coating surfaceof the coating extend in the longitudinal direction of the coating andare located parallel to each other, with a width of 0.5 μm to 200 μm. Inone embodiment, the pluralities of grooves on the inner coating surfaceof the coating have a maximal width of 1 μm to 30 μm. In one embodiment,the plurality of grooves on the inner coating surface of the coatinghave a maximal width of 2 μm to 15 μm, in particular 2 μm to 5 μm.

In one embodiment, the pluralities of grooves on the inner coatingsurface of the coating have a maximal width of 80 μm to 120 μm. In oneembodiment, the pluralities of grooves on the inner coating surface ofthe coating have a maximal width of approximately 100 μm.

In one embodiment, the plurality of grooves on the inner coating surfaceof the coating have a maximal width of 1 μm to 6 μm, in particular amaximal width of 2 μm to 5 μm. In one embodiment, the pluralities ofgrooves on the inner coating surface of the coating have a maximal widthof approximately 2 μm. The smaller grooves are preferred since thisspace influences the adhesion of progenitors as this space is congruentwith the surface receptor size and leads to forced adhesion.

The maximal width of the grooves is the maximal distance between oneside of the groove and the neighboring side of the same groove, measuredtransverse to the longitudinal extension direction of the sides.

In some embodiments, the grooves comprise a rectangular shape, asemicircle shape or a trapezoid shape. In some embodiments, the cornersof the applied shape of the grooves, in particular a rectangular shapeor a trapezoid shape, are rounded, allowing for a better laminar flow,which will be discussed below. In some embodiments, the grooves comprisea semicircle shape with a maximal width of 2 μm to 15 μm, in particular2 μm to 5 μm. In some embodiments, the grooves comprise a rectangularshape with each groove comprising essentially identical maximal widthsin the range of 2 μm to 15 μm, in particular 2 μm to 5 μm.

In some embodiments, the grooves comprise an upper width in the range of2 μm to 15 μm, in particular 2 μm to 5 μm, and a lower width in therange of 50% to 150%, in particular in the range of 80 % to 120%, of thesize of the upper width. The upper width is the distance between oneside of the groove and the neighboring side of the same groove, measuredalong the circumference of the inner diameter of the inner coatingsurface of the coating and the lower width is the distance between oneside of the groove and the neighboring side of the same groove, measuredtransverse to the longitudinal extension direction of the sides of thegroove and in the plane, in which the bottom of the grooves essentiallyexpands. Thus, the upper width is located near the circumference of theinner diameter of the inner coating surface of the coating and the lowerwidth is located at the bottom of the grooves. In some embodiments, thegrooves comprise a rectangular shape, a semicircle or trapezoid shapewith an upper width in the range of 2 μm to 15 μm, in particular 2 μm to5 μm and a lower width in the range of 50% to 150%, in particular in therange of 80% to 120%, of the size of the upper width.

Furthermore, the depth of the grooves, which is the distance from thecircumference of the inner diameter of the inner coating surface of thecoating to the bottom of the groove, is in the range of 2 μm to 15 μm,in particular 2 μm to 5 μm. In some embodiments, the upper width and thedepth of one groove are essentially the same. In some embodiments, theupper and lower width and the depth of one groove are essentially thesame.

In some embodiments, the upper and/or lower width and/or depth ofneighboring grooves are essentially the same. In some embodiments,neighboring grooves comprise different upper and lower widths and adifferent depth.

In some embodiments, the distance between neighboring grooves is under10 μm, in particular under 1 μm. In some embodiments, the distancebetween two neighboring grooves is essentially identical for theplurality of grooves. The distance between neighboring grooves is thedistance between one side of a groove and the neighboring side of aneighboring groove, measured along the circumference of the innerdiameter of the inner coating surface of the coating.

Generally, the coating will capture endothelial cells and progenitorcells. These cells will attach themselves on the inner side of thecoating. The main part of the captured cells will be progenitor cells,whereby endothelial cells will only be captured in the range of about1%, since the progenitor cells are easily available and are particularlymobilized after damage to a natural graft occurs. In general, the majorpart of the progenitor cells, which amounts to about 80%, originate fromthe periphery of the artificial vascular graft and migrate through the“holes” in the primary scaffold structure material or the semipermeableprimary scaffold structure material and the semipermeable coatingmaterial (see explanation above) and only a small part (20%) stems fromthe blood inside the artificial vascular graft. Progenitor cells (fromthe periphery) originate in general from the adventitia of neighboringtissue (the so called sca1+progenitors). Considering the aorta, most ofthe cells are encased in the respective wall.

Progenitor cells differentiate either to become endothelial cells or tobecome smooth muscle cells, depending on the conditions of the bloodflow inside the artificial vascular graft. The main conditions governingthis differentiation process are the amount of shear stress on aprogenitor cell and the amount of turbulent flow inside the artificialvascular graft. The higher the shear stress and the lower the turbulentflow, the higher the probability that a progenitor cell willdifferentiate to an endothelial cell (which is flat and spindle shaped).

The alignment and the form of the grooves in the longitudinal directionprevents a turbulent flow inside the artificial vascular graft, inparticular a turbulent flow directed essentially crosswise to thegrooves under conditions of blood flow inside the artificial vasculargraft after implantation. Thus, the plurality of grooves comprised inthe coating of the inner surface allows for an essentially laminar flowof blood, with no or only a minimum of turbulent flow.

In some embodiments, the shear stress inside the artificial vasculargraft is at least 1.5 Pa (dyn/cm²), in particular more than 2.5 Pa(dyn/cm²) under conditions of use of the artificial graft afterimplantation. Generally, the shear stress on a cell will increase fromthe position near the inner coating surface of the coating of theartificial vascular graft to the radial center of the artificialvascular graft. Thus, the more a cell is positioned near this center ofthe artificial vascular graft, the more shear stress will be exerted onthis cell. Therefore, the probability of a differentiation toendothelial cells will increase, the nearer a progenitor cell issituated to the radial center of the artificial vascular graft. Cellsthat are situated with the least distance to the symmetrical center of atubular shaped artificial vascular graft, will be referred to as luminalcells or cells in luminal position.

Given the combination of the near laminar flow and the shear stressinside the artificial graft captured progenitor cells specificallydifferentiate to endothelial cells at the luminal position or near theluminal position of the artificial graft and smooth muscle cells at theinner side of the coating. Thus, due to the capturing of progenitorcells and their differentiation, the artificial graft will—afterimplantation and subsequent differentiation of cells captured onto thegraft—comprise smooth muscle cells on the inner coating surface(situated on the primary scaffold structure) and endothelial cells onthese smooth muscle cells. Therefore, human endothelial cells arespecifically situated in the luminal position of the artificial graft.

Depending on the applied materials for the primary scaffold structureand the coating as well as the shape and diameter of the grooves, theconditions concerning the laminar flow and the shear stress can beselected in order to control the amount of endothelial cells and smoothmuscle cells. In some embodiments, the ratio of endothelial cells tosmooth muscle cells that differentiate from the captured progenitorcells is 2:1 after a period of 3 to 10 days, particularly after about 7days. In some embodiments, 5% to 15% of smooth muscle cells (positioneddirectly or at the vicinity of the coating) and 95% to 85% ofendothelial cells (positioned directly or at the vicinity of the luminalposition) will differentiate from the captured progenitor cells.

In general, after 30 min progenitor cells are being captured on theinner coating surface of coating. After 7 days around 60% of the area ofthe inner coating surface of the coating is colonized. The outer side ofthe coating will be covered by fibrin and then by fibroblasts containingscar tissue.

In one embodiment, the coating comprises as a coating material CollagenIV or a material with ECM components (extracellular matrix), whichallows a high capture rate of endothelial cells and progenitor cells onthe inner coating surface of the coating and a differentiation rate ofprogenitor cells to endothelial cells in a rate of essentially 100%.

In one embodiment, the coating comprises as a coating material CollagenIV to enhance cellular migration at the anastomosis site. Thus, thecoating comprises as one component Collagen IV. However, it may comprisefurther components such as cellulose or fibrin for providing anadditional stability and reducing the amount of expensive collagen IV.Alternatively Pluronic F 125 (CAS. No. 9003-11-6) und2-Octyl-Cyanoacrylat (CAS No. 133978-15-1) may be applied. Furtherexamples can be found in the experimental section.

In some embodiments, the coating comprises a structure pattern in formof pores. In some embodiments, such pores have a diameter of 50 nm to500 nm. In some embodiments, such pores have a diameter of 1 μm to 15μm. In some embodiments, the coating comprises a structure pattern inform of pores. In some embodiments, such pores have a diameter of 10 nmto 100 nm. The structure pattern allows—aside from the migrationability—for a higher capturing rate of endothelial cells and progenitorcells on the inner coating surface of the coating. In some embodiments,the coating material comprises cellulose with a structure pattern inform of pores.

In some embodiments, the cellulose material of the coating is sterile,inert and comprises semipermeable and anti-thrombogenic abilities, aswell as the above mentioned flexibility and compliance, whereby thecoating comprises a plurality of grooves on the inner coating surface ofthe coating with a maximal width in the range of about 1 μm to 50 μm. Insome embodiments, the coating consists of cellulose material, derivedfrom the bacteria Acetobacter, comprising the previously describedfeatures and the primary scaffold structure comprises a shape memoryalloy, in particular Nitinol. The primary scaffold structure and thecoating comprise a flexibility of 5% to 40%, in particular of 15% to20%, with respect to the original outer diameter of the primary scaffoldstructure or the original inner diameter of the coating, and acompliance in the range of 400 to 1000%/2.93 kPa (22 mm Hg), inparticular in the range of 600 to 800%/2.93 kPa (22 mm Hg).Additionally, the cellulose can comprise a structure pattern in form ofpores.

In one embodiment, the artificial vascular graft comprises a secondcoating on the inner coating surface of the coating, whereby the secondcoating comprises a plurality of grooves on the inner second coatingsurface of the second coating and the inner second coating surface ofthe second coating is facing towards the inner space of the artificialvascular graft. In one embodiment the second coating is Collagen IV.Reference is made to the above mentioned properties and materialsconcerning the primary scaffold structure and the coating. In someembodiments, the plurality of grooves are comprised on the inner secondcoating surface of the second coating and on the inner coating surfaceof the coating situated on the inner surface of the primary scaffoldstructure.

In one embodiment, the second coating comprises as a coating materialCollagen IV to enhance cellular migration at the anastomosis site.However, it may comprise further components such as cellulose or fibrinfor providing an additional stability and reducing the amount ofexpensive collagen IV.

The second coating may be applied in form of a spray comprising anamount of 90% Collagen IV and Fibrin, whereas the remaining 10% may bechosen from a Vascular Endothelial Growth Factor (VEGF) and PenicillinStreptomycin (Pen/Strep), or a suitable comparable material. The 90% ofCollagen IV and Fibrin may comprise 20-40% Collagen IV and 70% to 50%Fibrin, in particular 25-35% Collagen IV and 65% to 55% Fibrin, moreparticularly approximately 30% Collagen IV and approximately 60% Fibrin.Alternatively Pluronic F 125 (CAS. No. 9003-11-6) und2-Octyl-Cyanoacrylat (CAS No. 133978-15-1) instead of fibrin may beapplied.

Further examples can be found in the experimental section.

In some embodiments, the second coating comprises a thickness (wherebythickness is the difference between the inner diameter of the secondcoating and the inner diameter of the coating) in the range of 0.5 mm to5 mm, in particular in the range of 1 mm to 2 mm. The inner diameter ofthe second coating is the maximal distance of two points situated on theinner coating surface of the tubular second coating, measured throughthe center of the tubular second coating and in the plane, which extendsvertical to the longitudinal extension direction of the tubular secondcoating.

In one embodiment, the primary scaffold structure comprises a shapememory alloy with 50 to 60% Nickel (Reference) and 40-50% Titanium(Balance), in particular 54.5% to 57.0% Nickel (Reference) and43.0-45.5% Titanium (Balance) according to the Standard Specificationfor Wrought Nickel-Titanium Shape Memory Alloys for Medical Devices andSurgical Implants (ASTM F2063-05; Nitinol) and the coating materialcomprises cellulose material. According the characteristics andfunctions of the primary scaffold structure and the coating in form ofcellulose material reference is made to the above mentioned details.Additionally, the artificial vascular graft comprises a second coatingon the inner coating surface of the coating with Collagen IV as a secondcoating material, whereby the second coating comprises a plurality ofgrooves on the inner second coating surface. In an alternative, thecoating and the second coating comprise a plurality of grooves on theirinner surfaces. This allows for, if the artificial vascular graft isused as intended, a high capture rate of endothelial cells andprogenitor cells on the inner second coating surface of the secondcoating and a differentiation rate of progenitor cells to endothelialcells in a rate of essentially 100%, as discussed above. Reference isalso made to the above-mentioned properties concerning the plurality ofgrooves

By using an artificial vascular graft as intended an essentially laminarflow and a shear stress of at least 1.5 Pa (dyn/cm²), in particular morethan 2.5 Pa, is achieved. The applied primary scaffold, the coating aswell as the plurality of grooves allow that a specific amount of smoothmuscle cells could be differentiated and attached to the inner coatingsurface of the coating, namely 5% to 40%, in particular 5% to 15%,whereby the rest of the progenitor cells are differentiated to humanendothelial cells and are situated in or near the luminal position.Therefore, it is possible to accumulate only specific types of cells,namely human endothelial cells (as a major part) in the luminalposition, as well as smooth muscle cells in a specific and restrictedamount near the inner coating surface of the coating or the inner secondcoating surface of the second coating. Those cells provide very similarconditions compared to a human blood vessel inside the artificial graft.

By the in-vivo capturing and/or differentiation of endothelial cells afunctional endothelium is provided in the luminal position withanti-thrombogenic properties. Due to tight intercellular connections,the provided endothelium works as a semi-selective barrier between thelumen of the artificial vascular graft and surrounding tissue,controlling the passage of materials and the transit of white bloodcells into and out of the bloodstream.

Thus, the artificial graft, if is used as intended, is colonized in-vivoby the desired cells derived from the human body. There is norequirement for an external incubation or cell donation, which comprisean infection and repulsion risk. The artificial vascular graft could beused without a time delay and is compatible for every patient.

The artificial vascular grafts according to the invention comprisesimilar blood vessel qualities as a human blood vessel, including anappropriate physiological compliance and burst pressure in order towithstand hemodynamic pressure changes without failure and provide anappropriate response to physiological changes. These artificial vasculargrafts are highly compatible for each patient without the need foradditional medication, easy of use for the physician and comprisefurther an unproblematic storage and rapid availability. The artificialvascular graft comprises anti-thrombogenic and non-immunogenicproperties and is resistant to infection. Furthermore, the in-vivoprovision of a functional endothelium provides an integration of theartificial vascular graft into the vascular system without resulting inchronic inflammation, hyperplasia or fibrous capsule formation orthrombosis.

According to a second aspect the invention relates a method forproduction of an artificial vascular graft, in particular an artificialvascular graft according to any one of claims 1 to 11, which ischaracterized by the following steps:

-   -   a. providing a bioreactor comprising a cellulose producing        bacteria:    -   b. introducing a tubular primary scaffold structure into the        bioreactor, whereby said tubular primary scaffold structure        encompasses an inner space, and said primary scaffold structure        has an inner surface facing towards said inner space;    -   c. introducing a tubular structural component into said inner        space, whereby the distance between said inner surface and the        perimeter of said tubular structural component is in the range        of 0.5 mm to 6 mm, whereby said tubular structural component        comprises protruding structural elements, which are situated on        the perimeter of said tubular structural component and extend        along the longitudinal extension direction of said tubular        structural component, whereby said protruding structural        elements comprise a height in the range of about of 2 μm to 15        μm and a width in the range of about 1 μm to 50 μm;    -   d. covering of the primary scaffold structure with cellulose        providing a coating:    -   e. removal of the structural component from the primary scaffold        structure.

In one embodiment, the cellulose producing bacteria is provided in aliquid bacteria medium.

In some embodiments, the tubular primary scaffold structure and thetubular structural component are encompassed by the liquid bacteriamedium (e.g. by a vertical application). In some embodiments, thetubular primary scaffold structure and the tubular structural componentcan be in contact with pure oxygen (e.g by bubbling through the liquidmedia).

In one embodiment, the tubular primary scaffold structure and thetubular structural component are provided in a horizontal setting—withrespect to the surface of the liquid bacteria medium, whereby parts ofthe tubular primary scaffold structure and the tubular structuralcomponent are encompassed by the liquid bacteria medium and parts areencompassed by air. In some embodiments approximately 50% of the tubularprimary scaffold structure and the tubular structural component areencompassed by the liquid bacteria medium.

In some embodiments, the contact of said parts of the tubular primaryscaffold structure and the tubular structural component with the liquidbacteria medium and the air is changed periodically, in particular by arotating system attached to the tubular primary scaffold structure andthe tubular structural component.

In some embodiments, the rotation is set to 1 to 10 rounds per minute(rpm), in particular to 3 rpm to 8 rpm, more particularly toapproximately 6 rpm. A continuous rotation is preferred, providing amore evenly distribution of said cellulose.

In some embodiments, the temperature of the liquid bacteria medium andthe bioreactor is 26-28° Celsius.

In some embodiments, the culture time is in the range of 1 to 10 days,in particular approximately 2 to 8 days, more particularly approximately4 days.

The liquid bacteria medium may be exchanged if appropriate, inparticular every 24 hours.

In some embodiments, the air in the bioreactor comprises an enhancedamount of oxygen (more than 21%).

In some embodiments, the oxygen content in the air in the bioreactor isenhanced by a periodical addition of pure oxygen, in particular pureoxygen with an oxygen content of 99.5%, 99.95%, 99,995% or 99.999%. Insome embodiments, the oxygen content in the air in the bioreactor isenhanced by a periodical addition of pure oxygen every 6 hours. Apreferred level of oxygen is 65% up to 80% pure oxygen. The use of anenhanced amount of oxygen increases the stability of the cellulosecoating. With “normal” air a stability of 26.66 kPa (350 mm Hg) isachieved, whereas the use of an oxygen content of approximately 80%provides a stability of 133.32 kPa (1000 mm Hg).

The cellulose produced by the bacteria in the bioreactor will slowlycover the primary scaffold structure and the tubular structuralcomponent. After 5 to 7 days the primary scaffold structure, theprotruding elements and the perimeter of the tubular structuralcomponent are covered by the cellulose coating and the tubularstructural component is removed. After removal of the tubular structuralcomponent the protruding elements will effect a plurality of grooves—byway of negative impression—in the inner coating surface of the coating,whereby the rest of the inner coating surface of the coating willcomprise a tubular surface, due to the growth limitation in form of theperimeter of the tubular structural component.

The distance between the inner surface of the primary scaffold structureto the perimeter of the tubular structural component is measured in theplane, which extends vertical to the longitudinal extension direction ofthe primary scaffold structure. Thus, depending on the location of thesymmetrical center of the tubular structural component and thesymmetrical center of the primary scaffold structure, the distancebetween the inner surface of the primary scaffold structure to theperimeter of the tubular structural component may be different, viewedalong the circular path of the primary scaffold structure.

In one embodiment, the tubular structural component is placed inside theprimary scaffold structure, in such a way, that the symmetrical centerof the tubular structural component and the symmetrical center of theprimary scaffold structure are congruent. Thus, the distance between theinner surface of the primary scaffold structure to the perimeter of thetubular structural component is essentially the same, viewed along thecircular path of the primary scaffold structure. In other words, thesymmetrical center of the tubular primary scaffold structure and thetubular structural component are essentially in the same place.

The main body of the tubular structural component, comprising a definedouter diameter, is viewed as the perimeter of the tubular structuralcomponents. The protruding structural components, which are situated onthe perimeter of the tubular structural component, are not relevant inview of the above discussed distance. Thus, after coating of the primaryscaffold structure with cellulose, the inner diameter of the coatingwill be restricted by the outer diameter of the structural component.Depending on the applied diameter of the primary scaffold structure andthe desired inner diameter of the coating, as defined above, the outerdiameter of the tubular structural component can be chosen accordingly.For example, if a primary scaffold structure with an outer diameter (thethickness of the primary scaffold structure will be neglected in thisexample) of 6 mm is applied and a coating with an inner diameter of 4 mmis desired, the outer diameter of the tubular structural component willbe 2 mm.

Furthermore, the distance from the inner surface of the primary scaffoldstructure to the perimeter of the tubular structural component willrestrict the “inner” thickness of the coating material (measured fromthe inner surface of the primary scaffold structure towards the innercoating surface of the coating situated on the inner surface of theprimary scaffold structure). In one embodiment the “inner” thickness ofthe coating material is roughly the same as the “outer”thickness—measured from the outer surface of the primary scaffoldstructure to the outer coating surface of the coating material, situatedon the outer surface of the primary scaffold structure. In oneembodiment, the “outer” thickness of the coating material is higher thanthe “inner” thickness.

In one embodiment, the protruding structural elements are protrudingradially from the perimeter of the tubular structural component andcomprise the shape of protruding tracks, which extend parallel to eachother in the longitudinal extension direction of the structuralcomponent and comprises a maximal width of about 0.1 μm to 200 μm, inparticular 1 μm to 50 μm. In a further embodiment, the protruding trackson the perimeter of the tubular structural component have a maximalwidth of 1 μm to 30 μm. In one embodiment, the protruding tracks on theperimeter of the tubular structural component have a maximal width of 2μm to 15 μm, in particular 2 μm to 5 μm. The maximal width of theprotruding tracks on the perimeter of the tubular structural componentis the maximal distance between one side of the protruding tracks andthe neighboring side of the same protruding tracks, measured transverseto the longitudinal extension direction of the sides.

In some embodiments, the protruding tracks comprise a rectangular shape,a semicircle shape or a trapezoid shape. In some embodiments, thecorners of the applied shape of the protruding tracks, in particular arectangular shape or a trapezoid shape, are rounded. In someembodiments, the protruding tracks comprise a semicircle shape with amaximal width of 2 μm to 15 μm, in particular 2 μm to 5 μm. In someembodiments, the protruding tracks comprise a rectangular shape with amaximal width in the range of 2 μm to 15 μm, in particular 2 μm to 5 μm.

In some embodiments, the protruding tracks comprise a first width in therange of 2 μm to 15 μm, in particular 2 μm to 5 μm, and a second widthin the range of 50% to 150%, in particular in the range of 80% to 120%,of the size of the first width. The first width is the distance betweenone side of a protruding track and the neighboring side of the sameprotruding track, measured along the circumference of the outer surfaceof the tubular structural component and the second width is the distancebetween one side of a protruding track and the neighboring side of thesame protruding track, measured transverse to the longitudinal extensiondirection of the sides of the protruding track and in the plane, whichexpands through the points of the protruding track, which are situatedfurthest from the perimeter of the structural component. In someembodiments, the protruding tracks comprise a rectangular shape, asemicircle or trapezoid shape with a first width in the range of 2 μm to15 μm, in particular 2 μm to 5 μm and a second width in the range of 50% to 150%, in particular in the range of 80% to 120%, of the size of thefirst width.

Furthermore, the height of the protruding tracks, which is the distancefrom the perimeter of the tubular structural component to the point ofthe protruding track, which is situated furthest from the perimeter ofthe tubular structural component (in other words, the top of theprotruding track), measured transverse to the longitudinal extensiondirection of the tubular structural component, is in the range of 2 μmto 15 μm, in particular 2 μm to 5 μm. In some embodiments, the firstwidth and the height of one protruding track are essentially the same.In some embodiments, the first and second width and the height of oneprotruding track are essentially the same.

In one embodiment, the protruding tracks of the tubular structuralcomponent comprise a length in their longitudinal extension direction inthe range of at least the length of the primary scaffold structure.

In one embodiment, the tubular structural component is removed byapplying a force on the tubular structural component, whereby the forceis directed essentially along the longitudinal extension direction ofthe primary scaffolds structure. Thus, the tubular structural componentis removed along the longitudinal extension direction of the primaryscaffolds structure.

In one embodiment, the outer diameter of the tubular structuralcomponent is variably adjustable, in such a way that before the removalof the structural component the outer diameter of the structuralcomponent is minimized, so that the protruding elements of the tubularstructural component are removed vertical to the longitudinal extensiondirection of the tubular structural component from the coating material.The tubular structural component is subsequently removed along thelongitudinal extension direction of the primary scaffold structure, asdiscussed above. Thus, the structural component could be removed withoutfurther contacting the coating material.

In one embodiment, a second coating is applied to the cellulose coatingon the inner surface of said cellulose coating which comprises as acoating material Collagen IV to enhance cellular migration at theanastomosis site. Furthermore, the second coating may comprise furthercomponents such as fibrin for providing an additional stability. Furtherexamples can be found in the experimental section. The second coatingmay be applied in form of a spray.

In some embodiment, said spray may be applied after implantation of thegraft and completion of the anastomosis.

In one embodiment, the structural component can comprise the form of arod or a mandrel containing the protruding elements on the outer surface(perimeter) of the rod or mandrel.

Generally, any biologically acceptable material with the ability to beshaped into a tubular structure having the required compliance andflexibility—as discussed above—can be used for the primary scaffold.

In one embodiment, the primary scaffold structure comprises or consistsof a metal, a metal alloy, in particular a shape memory alloy, asdiscussed above.

In some embodiments, the primary scaffold structure comprises orconsists of a fibroblast sheet. In some embodiments, the primaryscaffold structure comprises or consists of an arterial, respectivelyvenous decelluarized homograft or xenograft.

In some embodiments, the primary scaffold structure comprises orconsists of a biostable polymeric material or a degradable polymermaterial, whereby the polymer could be a synthetic polymer or abiopolymer. Reference is made to the previous discussion of thesematerials.

In one embodiment, the primary scaffold structure comprises or consistsof a structured surface in form of a mesh structure. In someembodiments, the primary scaffold structure comprises a knitted, braidedor woven mesh structure or a wire mesh structure, as discussed above.

In some embodiments, the primary scaffold structure comprises orconsists of a shape memory polymer or an elastomeric synthetic polymer,as discussed above.

In one embodiment, the primary scaffold structure consists of a wiremesh structure, as discussed above. Due to the “holes” of the wire meshstructure, the cellulose will not only cover the primary scaffoldstructure, but also grow through the “holes” of the wire mesh, providinga strong connection between the primary scaffold structure and thecellulose coating.

In one embodiment, the primary scaffold structure consists of a wiremesh structure having a shape memory alloy as a primary scaffoldstructure material with 50 to 60% Nickel (Reference) and 40-50% Titanium(Balance), in particular 54.5% to 57.0% Nickel (Reference) and43.0-45.5% Titanium (Balance) according to the Standard Specificationfor Wrought Nickel-Titanium Shape Memory Alloys for Medical Devices andSurgical Implants (ASTM F2063-05; Nitinol). According thecharacteristics and functions of the primary scaffold structurereference is made to the above mentioned details.

In one embodiment, the cellulose is derived from the bacteriaAcetobacter and is sterile, inert and comprises semipermeable andanti-thrombogenic abilities, as well as the above discussed flexibilityand compliance.

In one embodiment, the cellulose is derived from the bacteriaAcetobacter and the primary scaffold structure consists of a wire meshstructure having a shape memory alloy as a primary scaffold structurematerial with 50 to 60% Nickel (Reference) and 40-50% Titanium(Balance), in particular 54.5% to 57.0% Nickel (Reference) and43.0-45.5% Titanium (Balance) according to the Standard Specificationfor Wrought Nickel-Titanium Shape Memory Alloys for Medical Devices andSurgical Implants (ASTM F2063-05; Nitinol). According thecharacteristics and functions of the primary scaffold structurereference is made to the above mentioned details.

In one embodiment, the cellulose is derived from the bacteriaAcetobacter, in particular Acetobacter xylinum strain ATTC 23769 and issterile, inert and comprises semipermeable and anti-thrombogenicabilities, as well as the above discussed flexibility and compliance.

Experimental Section:

TABLE 1 Glucosemedia: Acetobacter Xylinum medium with glucose 2.381% forproduction of cellulose base g/ base mg/ components percentage MW 1 L 2L 1 L 2 L KH₂PO₄ 0.7 7.00 g 14.00 g MgSO₄ × 7 H₂O 0.213 2.13 g 4.26 gH₃BO₃ 0.00043 0.0043 0.0086 4.3 mg 8.6 mg Nicotinamide 0.00007 0.00070.0014 0.7 mg 1.4 mg FeSO₄ × 7 H₂O 0.00095 0.010 0.019 9.5 mg 19.0 mgNa₂HPO₄ 0.134 142 1.34 g 2.68 g (NH₄)₂SO₄ 0.354 3.54 g 7.08 g Ethanolabs 0.473 4.73 ml 9.46 ml Glucose 50% 2.381 50 ml 100 ml Start a Glucose50%: 125 g in 250 ml MilliQ H₂O, filter sterile; Start a salinesolution, store overnight in the cold storage room. Add ethanol directlybefore autoclaving. Add the 50% Glucose solution after the autoclavingto the RT warm medium; KH₂PO₄—potassium dihydrogen orthophosphate(purum, Fluka, ref. nr. 60230); MgSO₄ × 7 H₂O—magnesia sulphateheptahydrate (Fluka, ref. nr. 63142); H₃BO₃—boracic acid (Fluka, ref.nr. 15660); Nicotinamide (cell culture tested, Sigma, ref. nr.N0636-100G); FeSO₄ × 7 H₂O—Ferrous sulphate Heptahydrat (Sigma, ref. nr.F8633-250G); Na₂HPO₄—disodium hydrogen phosphate (Sigma, ref. nr.S3264-500G); (NH₄)₂SO₄—Ammonium sulphate (Fluka, ref. nr. 09980);ethanol absolute (>99.8%), Fluka, ref. nr. 02860), the substances aredissolved in MilliQ H₂O (ISO 3696).

TABLE 2 Dissolve components/ingredients successively in MilliQ H₂O andthen it has to be filled in glass bottles and to be autoclaved (20 min.121° C.). Bacteriamedia: starter medium Actobacter xylinum % MW 1 L 2 LD(+) glucose waterfree Sigma 2 180.16 20.0 g  40.0 g proteose peptoneFluka, ref. nr. 0.5 5.0 g 10.0 g 29185-500G-F yeast extract; Sigma, ref.nr. 0.5 5.0 g 10.0 g Y1625-250G Na₂HPO₄ Sigma, ref. nr. 0.27 142 2.7 g 5.4 g S3264-500G Citric acid Sigma, ref. nr. 0.15 1.5 g  3.0 gC2404-100G

Example Concerning the Provision of a Cellulose Coating:

Provision of a bioreactor comprising a cellulose producing bacteria in aliquid bacteria medium according to the above mentioned tables (500 mlof liquid Acetobacter media). A tubular primary scaffold structure inform of a nitinol mesh is provided on a tubular structural component(mandril), with protruding structural elements. Both are arrangedhorizontally to the liquid media on the surface of said media in such away that approximately 50% of the mandril and the mesh are encompassedby the liquid bacteria medium and both are arranged rotatable in thebioreactor on a rotating.

By rotating the mandril and the mesh (with 6 rpm) parts of the mandriland the mesh are contacting the liquid bacteria medium and airperiodically. The oxygen content in the air in the bioreactor isenhanced by a periodical addition of pure oxygen every 6 hours.

The temperature of the liquid bacteria medium and the bioreactor is26-28° Celsius.

The media change every 24 hours and the mandril and the mesh are rotatedfor 4 days, providing a providing a coating. After that, the mandril isremoved providing a cellulose coating on the mesh, which comprisesgrooves on the inner surface by way of negative impression.

Second Coating:

The second coating may be applied in form of a spray, in particularafter implantation of the graft and completion of the anastomosis, toenhance cellular migration at the anastomosis site and if additionalstability is required. The spray may contain:

Fibrin 60%, Collagen IV 30% and the remaining 10% comprise VEGF(Vascular Endothelial Growth Factor) 25 ng/ml and 200 U/ml Pen/Strep(Penicillin Streptomycin “Pen/Strep” mixtures contain 5,000 units ofpenicillin (base) and 5,000 μg of streptomycin (base)/ml utilizingpenicillin G (sodium salt) and streptomycin sulfate in 0.85% saline.)

The invention is further illustrated by the following figures andexamples, from which further advantages and embodiments can be drawn.The figures and examples are not intended to limit the scope of theclaimed invention.

FIGURE LEGENDS

FIG. 1: Shows a schematic cross section view of an artificial vasculargraft 1 according to one aspect of the invention;

FIG. 2A: Shows a schematic cross section view of an artificial vasculargraft 1 according to a second aspect of the invention;

FIG. 2B: Shows an enhanced schematic cross section view of parts of thecoating 3 of the artificial vascular graft 1 of FIG. 2A;

FIG. 3: Shows a schematic cross section view of an artificial vasculargraft 1 according to a third aspect of the invention;

FIG. 4A-C: Show enhanced schematic cross section views of differentshapes of the plurality of grooves 4 situated on the inner coatingsurface 31 of a coating 3;

FIG. 5A-D: Show enhanced images of the plurality of grooves on the innercoating surface 31 of the coating 3 of an artificial vascular graft 1 indifferent enhancement levels, whereas A shows grooves with a width of 1μm (Type 1). B shows grooves with a width of 2 μm (Type 1), C showsgrooves with a width of 8 μm (Type 3), D shows grooves with a width of 8μm (Type 4), whereas visible “dots” are captured cells;

FIG. 6 Shows a diagram concerning the adhesion of cells on the innercoating surface 31 of the coating 3 of an artificial vascular graft 1measured in minutes (25 endothelial cells per quarter field of view inthe microscope) for the types 1, 2, 3, and 4 as depicted in FIG. 5A to D(x-axis) and type 5 (100 μm width of grooves).

REFERENCE LIST

1 vascular graft

2 primary scaffold structure

20 outer surface of the primary scaffold structure

21 inner surface of the primary scaffold structure

3 coating

30 outer coating surface of the coating

31 inner coating surface of the coating

4 grooves

7 second coating,

71 inner second coating surface of the second coating

8 inner space of the artificial vascular graft

A thickness of the primary scaffold structure

B inner thickness of the coating

C outer thickness of the coating

D depth of the grooves

N distance between neighboring grooves

L lower width of the grooves

U upper width of the grooves

W maximal width of the grooves

X outer diameter of the primary scaffold structure

Y inner diameter of the coating

FIGURES AND EXAMPLES

FIG. 1 shows a schematic cross section view of an artificial vasculargraft 1 according to one aspect of the invention.

The artificial vascular graft 1 comprises a primary scaffold structure2, which encompasses an inner space 8 of the artificial vascular graft1. The primary scaffold structure 2 has an inner surface 21 facingtowards the inner space 8 and an outer surface 20 facing away from theinner space 8. The artificial vascular graft 1 comprises further acoating 3 situated on the inner surface 21 of the primary scaffoldstructure 2. The coating 3 comprises further an inner coating surface 31facing towards the inner space 8 of the artificial vascular graft 1.Additionally, the artificial vascular graft 1 comprises a plurality ofgrooves (not shown due to reasons of clarity; concerning the pluralityof grooves on the inner coating surface 31 of the coating 3 reference ismade to FIGS. 2A and 2B) in said coating 3, which are situated on theinner coating surface 31 of the coating 3.

The primary scaffold structure 2 and the coating 3 comprise each asymmetrical, tubular shape with identical diameters throughout thetubular artificial vascular graft 1.

The primary scaffold structure 2 comprises a tubular shape with an outerdiameter X of about 3 mm for use as a small-size diameter artificialvascular graft 1. The outer diameter X is the maximal distance of twopoints situated on the outer surface 20 of the primary scaffoldstructure 2, measured through the center of the tubular primary scaffoldstructure 2 and in the plane, which extends vertical to the longitudinalextension direction of primary scaffold structure 2, whereby the outerdiameter X is depicted in FIG. 1, due to reasons of clarity, slightlyabove the center of the tubular primary scaffold structure 2. Thethickness A of the primary scaffold structure 2 (the difference betweenthe outer diameter X and the inner diameter of the primary scaffoldstructure 2) is about 0.2 mm. Concerning the outer diameter X and thethickness A of the primary scaffold structure 2, all the previouslydiscussed values may be employed.

The primary scaffold structure 2 comprises an inert, sterile,anti-thrombogenic and semipermeable polymer material. Reference is madeto the above discussed polymer materials.

The coating 3 comprises a tubular shape with an inner diameter Y ofabout 2 mm. The inner diameter Y is the maximal distance of two pointssituated on the inner coating surface 31 of the tubular coating 3,measured through the center of the tubular coating 3 and in the plane,which extends vertical to the longitudinal extension direction oftubular coating 3. The inner thickness B of the coating 3 (thedifference between the inner diameter of the primary scaffold structure2 and the inner diameter Y of the coating 3) is about 0.8 mm. Concerningthe inner diameter Y and the inner thickness B of the coating 3, all thepreviously discussed values may be employed.

The coating 3 consists of an inert, sterile, anti-thrombogenic andsemipermeable polymer material. Reference is made to the above discussedpolymer materials.

The primary scaffold structure 2 and the coating 3 comprise a complianceof 600%/2.93 kPa (22 mm Hg), a flexibility of 15% and a burst pressurehigher than 133.32 kPa. Other materials with a compliance andflexibility according to the above discussed characteristics may beapplied.

Therefore, the primary scaffold structure 2 and the coating 3 comprisesimilar mechanical properties as the native counterpart and provide aresponse to physiological changes by means of adequate vasoconstrictionand relaxation, if it is used as intended. They function without unduebulging or aggravated mismatching phenomena leading to graft failure.Concerning the characteristics of the grooves 4, reference is made tothe discussion of FIGS. 2A and 2B.

FIGS. 2A and 2B show a schematic crass section view of an artificialvascular graft 1 according to a second aspect of the invention and anenhanced schematic cross section view of the coating 3 of the artificialvascular graft 1 of FIG. 2A comprising a plurality of grooves 4.

The artificial vascular graft 1 comprises a tubular primary scaffoldstructure 2, which encompasses an inner space 8 of the artificialvascular graft 1. The maximal width of the grooves primary scaffoldstructure 2 has an inner surface 21 facing towards the inner space 8 andan outer surface 20 facing away from the inner space 8. The artificialvascular graft 8 comprises further a coating 3, which encloses theprimary scaffold structure 2. The coating 3 comprises an inner coatingsurface 31 facing towards the inner space 8 of the artificial vasculargraft 1 and an outer coating surface 30 facing away from the inner space8 of the artificial vascular graft 1.

Additionally, the artificial vascular graft 1 comprises a plurality ofgrooves 4 (which will be shown in FIG. 2B) in the coating 3, which aresituated on the inner coating surface 31 of the coating 3.

The primary scaffold structure 2 and the coating 3 comprise each asymmetrical tubular structure with identical diameters throughout thetubular artificial vascular graft 1.

The primary scaffold structure 2 comprises a tubular shape with an outerdiameter X (as defined previously) of about 4 mm for use as a small-sizediameter artificial vascular graft 1, whereby the outer diameter X isdepicted in FIG. 2, due to reasons of clarity, slightly above the centerof the tubular primary scaffold structure 2. The thickness A of theprimary scaffold structure 2 (the difference between the outer diameterX and the inner diameter of the primary scaffold structure 2) is about0.2 mm. Concerning the outer diameter X and the thickness A of theprimary scaffold structure 2, all the previously discussed values may bealso employed.

The coating 3 comprises a tubular shape with an inner diameter Y (asdefined previously) of about 2.5 mm. The inner thickness B (thedifference between the inner diameter of the primary scaffold structure2 and the inner diameter Y of the coating 3) and the outer thickness Cof the coating 3 (the difference between the outer diameter X of theprimary scaffold structure 2 and the outer diameter of the coating 3) isabout 0.8 mm. Different values of the inner diameter Y, inner thicknessB and outer thickness C of the coating 3 may be applied.

The primary scaffold structure 2 consists of a Nitinol-mesh withflexibility of 20%, compliance in the range of 700%/2.93 kPa (22 mm Hg)and burst pressure higher than 133.32 kPa. The Nitinol mesh comprises awire mesh structure, whereby the maximal distance between neighboringwires ranges from about 35 μm to 50 μm. Thus, the wire mesh structureprovides “holes” in the surface with an area of up to 2 500 μm². Othermaterials or other wires with different characteristics, as previouslydiscussed, may be applied.

The coating 3 consists of an inert, sterile, anti-thrombogenic andsemipermeable cellulose, derived from the bacteria Acetobacter. Thecoating 3 comprise further a compliance of 700%/2.93 kPa, a flexibilityof 20% and a burst pressure higher than 133.32 kPa. Other materials witha compliance and flexibility according to the above discussedcharacteristics may be applied. Thus, the coating material is compatiblefor every patient and there is no need for additional anticoagulationand the artificial vascular graft is able to recoil in order to preventaneurysm formation and exhibits a physiological compliance comparable toa native vessel in order to withstand hemodynamic pressure changeswithout failure, if the artificial vascular graft is used as intended.

The flexibility of the primary scaffold structure 2 and the coating 3allow a shear stress of more than 2.5 Pa, if the artificial vasculargraft is used as intended. Reference is made to the previous discussionfor further details.

Therefore, the primary scaffold structure 2 and the coating 3 comprisesimilar mechanical properties as the native counterpart and provide aresponse to physiological changes by means of adequate vasoconstrictionand relaxation, if it is used as intended. They function without unduebulging or aggravated mismatching phenomena leading to graft failure.

Furthermore, the cellulose material of the coating 3 reaches through the“holes” of the mesh structure of the primary scaffold structure 2allowing a strong connection between the primary scaffold structure 2and the coating 3. Thus, providing a necessary stability after apotential cutting of the artificial vascular graft 1 (no parts of themesh of the primary scaffold structure will come in contact with livingtissue, due to the coating 3, in which the primary scaffold structure 2is completely embedded).

Additionally, the mesh structure of the primary scaffold structure 2 andthe semipermeable cellulose material of the coating 3 allow, if thegraft is used as intended, only a migration of a specific type of cellsand gases from the outside of the artificial vascular graft 1 to theinner space 8 of the artificial vascular graft 1. Particularly O₂ andCO₂, vascular growth factors, all humoral agents, progenitor cellscapable of differentiating towards endothelial lineages and macrophages,are allowed to migrate through the primary scaffold structure 2 and thecoating 3 to the inner coating surface 31 of the coating 3, whereby thecoating 3 remains impermeable for the remaining substances of blood.Thus, the coating 3 functions as a selective barrier inside theartificial vascular graft 1.

Furthermore, the inner coating surface 31 of the coating 3 comprises aplurality of grooves 4 (FIG. 2B), which extend along the longitudinalextension direction of the tubular coating 3 and are located parallel toeach other. The number or the grooves is only a schematic example, dueto clarity reasons.

The plurality of grooves 4 on the inner coating surface 31 of thecoating 3 have a maximal width W of about 5 μm. The maximal width W ofthe grooves 4 is the maximal distance between one side of the groove 4and the neighboring side of the same groove 4, measured transverse tothe longitudinal extension direction of the sides. Furthermore, thedepth D of the grooves 4, which is the distance from the circumferenceof the inner coating surface 31 of the coating 3 to the bottom of thegroove 4, is about 2 μm. The distance N between neighboring grooves isabout 1 μm. The distance N between neighboring grooves is the distancebetween one side of a groove and the neighboring side of a neighboringgroove, measured along the circumference of the inner coating surface 31of the coating 3.

If the artificial vascular graft 1 is used as intended, progenitor cellsand endothelial cells (in a small amount) are captured at the innercoating surface 31 of the coating 3. Progenitor cells differentiate toendothelial or smooth muscle cells depending on the conditions insidethe artificial vascular graft 1. Two of the main conditions are theshear stress on a progenitor cell and the amount of turbulent flowinside the artificial vascular graft 1. Reference is made to theprevious discussion for further details.

The alignment and the form of the groves 4 in the longitudinal direction(in other words in the direction of the blood flow) prevents a turbulentflow inside the artificial vascular graft 1, in particular a turbulentflow, which is directed essentially crosswise to the grooves 4.

In general, the higher the shear stress and the lower the turbulentflow, the higher the chances that a progenitor cell will differentiateto an endothelial cell. On the other hand, the more turbulent flowresides inside the artificial vascular graft 1 and the lower the shearstress on the progenitor cells, the higher the chances that thedifferentiation to smooth muscle cells occurs. Given the combination ofthe near laminar flow and the shear stress on the progenitor cells atthe luminal position or near the luminal position, the progenitor cellsin these positions will differentiate to endothelial cells, whereby theprogenitor cells near the coating 3 will differentiate to smooth musclecells, due to the lower shear stress.

The artificial vascular graft 1 of FIGS. 2A and 2B allows, if it is usedas intended, that around one third smooth muscle cells (positioneddirectly or at the vicinity of the coating) and two thirds ofendothelial cells (positioned directly or at the vicinity of the luminalposition) will differentiate from the captured progenitor cells after aperiod of 3 to 10, particularly 7 days.

By the in-vivo capturing and/or differentiation of endothelial cells afunctional endothelium is provided in the luminal position withanti-thrombogenic properties. Due to tight intercellular connections,the provided endothelium works as a semi-selective barrier between thelumen of the artificial vascular graft and surrounding tissue,controlling the passage of materials and the transit of white bloodcells into and out of the bloodstream. The artificial vascular graft 1could be used without a time delay and is compatible for every patientand comprise similar blood vessel qualities as a human blood vessel,including an appropriate physiological compliance, flexibility and burstpressure in order to withstand hemodynamic pressure changes withoutfailure and provides an appropriate response to physiological changesand anti-thrombogenic and non-immunogenic properties. The artificialvascular graft 1 comprises an unproblematic storage and rapidavailability.

FIG. 3 shows a schematic cross section view of an artificial vasculargraft according to a third aspect of the invention. The artificialvascular graft 1 of FIG. 3 is similar to the previously discussedartificial vascular graft 1 of FIGS. 2A and B. Reference is made to thedetails discussed in FIGS. 2A and 2B.

The main difference is, that the artificial vascular graft 1 of FIG. 3comprises a second coating 7, consisting of Collagen IV, on the innercoating surface 31 of the coating 3, whereby the second coating 7comprises a plurality of grooves 4 (not shown for reasons of clarity) onthe inner second coating surface 71 of the second coating 7 and theinner second coating surface 71 of the second coating 7 is facingtowards the inner space 8 of the artificial vascular graft 1.

Collagen IV as a second coating 7 material allows for, if the artificialvascular graft is used as intended, a high capture rate of endothelialcells and progenitor cells on the inner second coating surface 71 of thesecond coating 7 and a differentiation rate of progenitor cells toendothelial cells in a rate of essentially 100%, as discussed above.Reference is made to the previously discussed properties concerning theplurality of grooves.

FIG. 4A-C show enhanced schematic cross section views of differentshapes of the plurality of grooves 4 situated on the inner coatingsurface 31 of a coating 3.

FIG. 4A shows a plurality of grooves 4 with a rectangular shape. Thegrooves 4 comprise an upper width U in the range of 2 μm to 15 μm, inparticular 2 μm to 5 μm. The upper width U is the distance between oneside of a groove 4 and the neighboring side of the same groove 4,measured along the circumference of the inner coating surface 31 of thecoating 3, and a lower width L, which is located at the bottom of agroove 4 and measured transverse to the longitudinal extension directionof the sides of the groove and in the plane, in which the bottom of thegroove 4 expands. The lower width L is in the range of 50% to 150%, inparticular in the range of 80% to 120%, of the size of the upper widthU. The depth D of the grooves 4, which is the distance from thecircumference of the inner coating surface 31 of the coating 3 to thebottom of the groove 4, is in the range of 2 μm to 15 μm, in particular2 μm to 5 μm. The distance N between neighboring grooves is under 10 μm,in particular under 1 μm. The distance N between neighboring grooves isthe distance between one side of a groove 4 and the neighboring side ofa neighboring groove 4′, measured along the circumference of the innercoating surface 31 of the coating 3.

FIG. 4B shows a plurality of grooves 4 with a partially rounded,rectangular shape. Concerning the definition and the parameters of theupper width U, lower width L, depth D and distance N, reference is madeto the description of FIG. 4A.

FIG. 4C shows a plurality of grooves 4 with a trapezoid shape.Concerning the definition and the parameters of the upper width U, lowerwidth L, depth D and distance N, reference is made to the description ofFIG. 4A.

FIG. 4A-C show only examples. Different shapes may be applied.Furthermore, the upper and/or lower width and/or depth of neighboringgrooves can be essentially the same. Some grooves may comprise differentupper and/or lower width and/or depth than a neighboring groove.

1. An artificial vascular graft (1) comprising a primary scaffold structure (2) encompassing an inner space (8) of the artificial vascular graft (1), said primary scaffold structure (2) having a. an inner surface (21) facing towards said inner space (8) and b. an outer surface (20) facing away from said inner space (8) and c. a coating (3) on said inner surface (21) and on said outer surface (20) characterized in that a plurality of grooves (4) is comprised in said coating (3) of said inner surface (21) and said primary scaffold structure (2) and said coating (3) on said inner surface (21) and on said outer surface (20) are designed in such a way that cells, in particular progenitor cells, can migrate through said outer surface (20) of said coating (3), said primary scaffold structure (2) and said inner surface (21) of said coating (3) to said inner space (8).
 2. The artificial vascular graft according to claim 1, wherein the primary scaffold structure (2) and/or the coating (3) is characterized by a tubular shape.
 3. The artificial vascular graft according to claim 2 characterized in that the primary scaffold structure (2) has an outer diameter (X) in the range of about 1.5 mm to 40 mm, in particular in the range of about 1.5 mm to 15 mm, and the coating (3) has an inner diameter (Y) in the range of about 1 mm to 35 mm, in particular in the range of about 3.5 mm to 5 mm.
 4. The artificial vascular graft according to claim 1 characterized in that the primary scaffold structure (2) and/or the coating (3) comprise a material, which is characterized by a compliance in the range of 400 to 1000%/2.93 kPa, in particular in the range of 600 to 800%/2.93 kPa.
 5. The artificial vascular graft according to claim 1 characterized in that the primary scaffold structure (2) and/or the coating (3) comprise a material, which is able to recoil to an original state after a symmetrical, radial expansion perpendicular to the longitudinal axis of the artificial vascular graft (1), wherein said radial expansion is in the range of 5% to 40%, in particular of 15% to 20%, with respect to the original outer diameter (X) of the primary scaffold structure (2) or the original inner diameter (Y) of the coating (3).
 6. The artificial vascular graft according to claim 1 characterized in that the primary scaffold structure (2) comprises holes or a mesh structure.
 7. The artificial vascular graft according to claim 1 characterized in that the primary scaffold structure (2) comprises a metal or metal alloy, in particular a shape memory alloy.
 8. The artificial vascular graft according to claim 1 characterized in that the primary scaffold structure (2) and/or the coating (3) comprise a polymer material, in particular a cellulose material.
 9. The artificial vascular graft according to claim 1 characterized in that the coating (3) comprises a structure pattern in form of pores with a diameter of 50 nm to 500 nm.
 10. The artificial vascular graft according to claim 1 characterized in that the coating (3) comprises an inner coating surface (31), which is facing towards the inner space (8) of the artificial vascular graft (1) and the coating (3) comprises a second coating (7) on said inner coating surface (31), particularly a second coating (7) comprising Collagen IV.
 11. The artificial vascular graft according to claim 1 characterized in that essentially each groove of the plurality of grooves (4) has a width (W) of 0.5 μm to 200 μm, in particular of 1 μm to 50 μm, more particularly of 2 μm to 5 μm.
 12. A method for production of an artificial vascular graft, in particular an artificial vascular graft according to claim 1, comprising the following steps: a. providing a bioreactor comprising a cellulose producing bacteria; b. introducing a tubular primary scaffold structure (2) into the bioreactor, whereby said tubular primary scaffold structure (2) encompasses an inner space, and said primary scaffold structure (2) has an inner surface (21) facing towards said inner space: c. introducing a tubular structural component into said inner space, whereby the distance between said inner surface (21) and the perimeter of said tubular structural component is in the range of 0.5 mm to 6 mm, whereby said tubular structural component comprises protruding structural elements, which are situated on the perimeter of said tubular structural component and extend along the longitudinal extension direction of said tubular structural component, whereby said protruding structural elements comprise a height in the range of about of 2 μm to 15 μm and a width in the range of about 1 μm to 50 μm; d. covering of the primary scaffold structure (2) with cellulose providing a coating (3); e. removal of the structural component from the primary scaffold structure (2).
 13. The method according to claim 12, wherein the primary scaffold structure (2) comprises features as defined in any one of the claims 2 to 8 and the coating (3) comprises features as defined in any one of the claims 2 to 5 or 8 to
 11. 